There could be some original characters as well. For example, a foreign kunoichi who comes to the village and is immediately drawn to Naruto. She could add a new cultural element to the harem. Another potential character could be an older female ninja who has seen Naruto grow up and now realizes she has feelings for him, which would add a more complex and perhaps controversial dynamic to the 'naruto x naruko harem' situation.
Sakura could be a potential character. She has a long - standing relationship with Naruto, and in this harem scenario, she might be jealous of Naruko at first but then come to accept the situation. Hinata could also be part of it. Given her love for Naruto, she would be an interesting addition to the harem, adding a shy and gentle dynamic.
Tenten could be in the fanfiction. She's a strong - willed and skilled kunoichi. Her presence in the harem could bring a different perspective as she might challenge Naruto in terms of weapon - based combat skills. Ino could also be there. With her mind - control abilities, she could create some interesting situations in the harem, like trying to use her jutsu to get Naruto's attention in a unique way.
Kakashi could also be a character in 'naruto and naruko harem fanfiction'. He can be the mentor figure, guiding Naruto and Naruko through different situations. His wisdom can influence how the harem relationships develop, for example, by giving Naruto advice on how to handle multiple relationships in a proper way.
Obviously, Naruto and Naruko are the main characters. Naruto, with his determination and unique abilities. And Naruko, who likely has her own charm and skills in this fanfiction.
Sakura could be an interesting addition. She might be jealous at first when she sees Naruto in a harem situation with Tayuya but then realizes she also has feelings for Naruto in a different way. Another character could be Ino. She could be friends with Tayuya and get drawn into the harem dynamic, adding more complexity to the relationships.
Her friends are likely to be part of it. A close female friend could be like a pregnancy buddy, sharing her own experiences if she has any. There might also be a mentor - like figure, an older woman who has been through pregnancy and can give Naruko valuable advice on everything from childbirth to raising a child.
One possible plot could be that Naruto and Naruko (assuming it's an alternate universe where there's a female version of Naruto) discover a new and powerful bloodline ability within their Uzumaki lineage. They might have to train together to master it and then use it to protect the village from a new threat. Maybe it's a bloodline ability that allows them to manipulate time on a small scale, like slowing down an enemy's attack.
For Naruto, you can develop his character by having him face new challenges related to his relationship with Narumi and Naruko. For example, he might struggle with how to balance his friendship with both of them. Narumi could be developed by giving her a backstory that ties into the Naruto universe in a unique way, like she has a family connection to an old ninja clan. And for Naruko, you can explore her more feminine side in contrast to Naruto's more brash nature, especially when it comes to her interactions with Narumi.
For Naruto, you could show his growth in terms of his leadership skills when he's with Naruko and Kushina. He could learn to be more patient and understanding, especially when Naruko might have a different approach to things. For Naruko, her character could be developed by showing her struggle to be recognized in a world where Naruto already has a reputation. Kushina could be developed by exploring her motherly side more deeply, as she interacts with both Naruto and Naruko.
One potential antagonist could be a rogue ninja from another dimension who wants to use Naruto and Naruko's abilities for his own gain. He might be jealous of their power and try to trap them in different dimensions to study their techniques. Another could be a powerful entity that controls the portals between dimensions and doesn't want Naruto and Naruko messing around with the balance of different worlds.
Hinata could be a potential member. She has always had a crush on Naruto. Her gentle and shy nature would add an interesting dynamic to the harem, especially when contrasted with Guren's more assertive personality.
In this fanfiction, Naruto and Naruko's characters can be developed through their shared experiences. They could face discrimination or special treatment because they are twins. Naruto, who is used to being an outcast, might handle it one way, while Naruko could have a different reaction. This would lead to them growing as individuals and as a pair. They could also develop by learning from each other's mistakes. For instance, if Naruto rushes into a fight, Naruko could teach him the value of planning, and Naruto could show her the importance of believing in oneself no matter what.